Ammonium sulfate is produced as a by-product from many processes for producing organic materials. In particular, a common method of producing oximes is to oximate an aldehyde or ketone with aqueous hydroxylamine salts under pH conditions such as 5-8. Exemplary processes are included in U.S. Pat. Nos. 3,873,624 and 3,931,331 to Mathew et al. Frequently, the hydroxylamine salt used is hydroxylamine sulfate, sometimes drawn as (H.sub.2 NOH).sub.2.H.sub.2 SO.sub.4 or (H.sub.3 NOH).sub.2 SO.sub.4 and the pH is raised by using gaseous ammonia. Under such conditions, the product oxime, ammonium sulfate and water are produced. Most oximes are relatively insoluble or immiscible with water such that a phase separation occurs. The bulk of the ammonium sulfate is present in an easily separated first aqueous layer which is removed. Thereafter, the product is purified from the remaining material (the second or organic layer) by one or more distillations such as a lites distillation to remove various by-products and then, unless the product is relatively high boiling, a product distillation to recover the oxime in the overhead.
It has been found that, in spite of the removal of most of the ammonium sulfate as a solution in a separate first layer, sufficient ammonium sulfate remains as an aqueous discontinuous layer in the second layer to complicate later purification techniques. Thus, when the organic material is subjected to lites distillation, particularly if substantial quantities of water are removed by lites distillation, then any ammonium sulfate present in the discontinuous phase can crystallize out of the remaining liquid. These crystals can coat equipment, block filters and other devices and complicate the remaining separation in various ways.
Accordingly, it is an object of this invention to recover the organic, substantially water-insoluble oxime product with a substantially reduced ammonium sulfate content prior to any distillation so as to prevent problems associated with ammonium sulfate crystallization.